Add-drop optical spectrum-division multiplexer

Abstract

An add-drop optical spectrum-division multiplexer for dropping a drop multiplex from an incoming multiplex signal and for adding an add multiplex into an outgoing multiplex signal. The multiplexer includes a demultiplexing device for separating a number of optical carriers from the incoming multiplex signal and for selecting drop carriers which constitute the drop multiplex as well as through carriers which are to be output as the outgoing multiplex signal. The multiplexer further includes an apparatus for selecting a certain number of add carriers from the total number of carriers of the add multiplex, and a coupling device and wavelength converter for allocating fixed wavelengths to the signals which modulate the through carriers and the add carriers.

We claim: 
     
       1. An add-drop optical spectrum-division multiplexer for dropping a drop multiplex from an incoming multiplex, and for adding an add multiplex to an outgoing multiplex, the multiplexer comprising: spectrum-division demultiplexing means for separating N number of carriers from the incoming multiplex, said incoming multiplex having no more than N number of carriers;   spectrum-division multiplexing means for multiplexing N number of carriers, thereby constituting an outgoing multiplex; and   coupling means for coupling the demultiplexing means to the multiplexing means;   the spectrum-division demultiplexing means and the coupling means comprise: an optical broadcaster for receiving the incoming multiplex and reproducing said incoming multiplex on at least N number of outlets;   at least N number of tunable filters coupled respectively to the N number of outlets of the broadcaster to select T number of through carriers from the incoming multiplex, where the number T is variable and not greater than N;   selection means for selecting, amongst no more than N number of demultiplexed carriers, E number of carriers and constituting the drop multiplex, the number E being variable and not greater than N;   selection means for selecting, from amongst the carriers constituting the add multiplex, I number of add carriers, the number I being variable and not greater than N;   means for supplying the multiplexing means with T number of new carriers having T number of respective different wavelengths selectable from N number of fixed wavelengths, and being respectively modulated by the signals modulating the T number of through carriers; and   means for supplying the multiplexing means with I number of new optical carriers having I number of respective different wavelengths selectable from the N number of fixed wavelengths and different from the T number of wavelengths selected for the signals modulating the T number of through carriers, said I number of new wavelengths being modulated by the signals modulating the I number of add carriers.     
     
     
       2. A multiplexer according to claim 1, wherein the means for selecting E number of drop carriers comprises means for enabling each of the carriers of the incoming multiplex to be directed simultaneously to the drop multiplex and to the means for supplying T number of new optical carriers. 
     
     
       3. A multiplexer according to claim 1, further comprising switch means for enabling any carrier in the add multiplex to be selected and passed through to the outgoing multiplex. 
     
     
       4. A multiplexer according to claim 1, wherein the means for supplying T number of new optical carriers to the multiplexing means, and the means for providing I number of new optical carriers to the multiplexing means comprise: common conversion means for converting no more than N number of wavelengths; and   common coupling means for coupling the selection means for selecting T number of through carriers to said conversion means, and the selection means for selecting I number of add carriers;   in that the selection means for selecting I number of add carriers selects the add carriers and transmits them to the common conversion means so as to allocate one of the fixed wavelengths to each of the signals modulating the add carriers; and   in that the N filters for selecting T number of through carriers selects demultiplexed carriers and transmits them to the common conversion means so as to allocate one of the fixed wavelengths to each of the signals modulating the through carriers.   
     
     
       5. A multiplexer according to claim 4, wherein the common coupling means comprises N number of optical switches each having two inlets and two outlets, a first outlet of each switch being connected to an inlet of the conversion means, and a second outlet being connected to the drop multiplex. 
     
     
       6. A multiplexer according to claim 4, wherein the common coupling means comprise N passive couplers each having two inlets and one outlet; the two inlets being connected respectively to one outlet of the selection means for selecting T number of through carriers, and to one outlet of the selection means for selecting I number of add carriers. 
     
     
       7. A multiplexer according to claim 1, wherein the means for supplying T number of new carriers to the multiplexing means comprise: first conversion means for converting the respective wavelengths of not more than N number of through carriers to the fixed wavelengths and having inlets directly connected to the outlets of N number of filters for selecting T number of through carriers; and   switch means co-operating with the first conversion means to allocate one of the fixed wavelengths to each of the signals modulating the through carriers; and   the means for supplying I number of new optical carriers to the multiplexing means comprise: second conversion means that are distinct from the first conversion means, for converting the respective wavelengths of not more than N number of add carriers to the fixed wavelengths, having inlets connected directly to the outlets of the selection means for selecting I number of add carriers; and   switch means co-operating with the second conversion means to allocate one of the fixed wavelengths to each of the modulating signals carried by the add carriers.     
     
     
       8. An add-drop optical spectrum-division multiplexer for dropping a drop multiplex from an incoming multiplex, and for adding an add multiplex to an outgoing multiplex, the multiplexer comprising: spectrum-division demultiplexing means for separating N number of carriers from the incoming multiplex, said incoming multiplex having no more than N number of carriers;   spectrum-division multiplexing means for multiplexing N number of carriers, thereby constituting an outgoing multiplex; and   coupling means for coupling the demultiplexing means to the multiplexing means;   the spectrum-division demultiplexing means and the coupling means comprise: an optical broadcaster which receives the incoming multiplex and reproducing the incoming multiplex on at least N number of outlets;   a first set of N tunable filters coupled to respective ones of the N number of outlets from the broadcaster to select, in the incoming multiplex, E number of drop carriers and T number of through carriers where the numbers T and E are variable and not greater than N;   a second set of N number of tunable filters for selecting, for the carriers constituting the add multiplex, I number of add carriers, the number I being variable and not greater than N;   N number of wavelength converters for providing the multiplexing means with T number of new carriers respectively modulated by the signals modulating the T number of through carriers, and I number of new optical carriers modulated by the signals modulating the I number of add carriers, said N number of new carriers having N number of different wavelengths; and   N number of optical switches each having two inlets and two outlets, and each having: a first inlet connected to an outlet of a respective filter of the first set;   a second inlet connected to an outlet of a respective filter of the second set;   a first outlet connected to the inlet of a respective one of the wavelength converters; and   a second outlet providing a drop carrier to the drop multiplex;   and in that the multiplexing means includes an N-inlet optical combiner having its inlets connected to the outlets of respective ones of the N number of wavelength converters.       
     
     
       9. An add-drop optical spectrum-division multiplexer for dropping a drop multiplex from an incoming multiplex, and for adding an add multiplex to an outgoing multiplex, the multiplexer comprising: spectrum-division demultiplexing means for separating N number of carriers from the incoming multiplex, said incoming multiplex having no more than N number of carriers;   spectrum-division multiplexing means for multiplexing N number of carriers, thereby constituting an outgoing multiplex; and   coupling means for coupling the demultiplexing means to the multiplexing means;   the spectrum-division demultiplexing means and the coupling means comprise: an optical broadcaster for receiving the incoming multiplex and reproducing said incoming multiplex on N number of outlets;   a first set of N number of tunable filters coupled to the N number of respective outlets of the broadcaster to select, from the incoming multiplex, E number of drop carriers;   a second set of N number of tunable filters coupled to the N number of respective outlets of the broadcaster to select from the incoming multiplex T number of through carriers;   a third set of N number of tunable filter for selecting, from the carriers constituting the add multiplex I number of add carriers, the number I being variable and not greater than N;   N number of passive couplers each having two inlets and one outlet, the two inlets being respectively connected to the outlet of a filter in the second set and to the outlet in the of a filter in the third set; and   N number of wavelength converters for providing the multiplexing means with T+I number of new carriers respectively modulated by the signals modulating the T number of through carriers and the I number of add carriers, where the sum T+1 is not greater than N; and   the multiplexing means include an N inlet optical combiner whose N number of inlets are connected to respective outlets from the N number of wavelength converters.     
     
     
       10. An add-drop optical spectrum-division multiplexer for dropping a drop multiplex from an incoming multiplex, and for adding an add multiplex to an outgoing multiplex, the multiplexer comprising: spectrum-division demultiplexing means for separating N number of carriers from the incoming multiplex, said incoming multiplex having no more than N number of carriers;   spectrum-division multiplexing means for multiplexing N number of carriers, thereby constituting an outgoing multiplex; and   coupling means for coupling the demultiplexing means to the multiplexing means;   the spectrum-division demultiplexing means and the coupling means comprise: an optical broadcaster for receiving the incoming multiplex and reproducing said incoming multiplex on N number of outlets;   a first set of N number of tunable filters coupled to respective ones of the N number of outlets of the broadcaster to select E number of drop carriers from the incoming multiplex, and for selecting T number of through carriers therefrom, the numbers T and E being variable and not greater than N;   a second set of N number of tunable filters coupled to respective ones of the N number of outlets of the broadcaster to select T number of through carriers from the incoming multiplex;   a third set of N number of tunable filters for selecting, from the carriers constituting the add multiplex, I number of add carriers, where the number I is variable and not greater than N;   N number of wavelength converters each having one inlet connected to an outlet from a respective filter of the first set, to provide the multiplexing means with T number of new carriers respectively modulated by the signals modulating the N number of through carriers; and   N number of wavelength converters for providing the multiplexing means with I number of new carriers respectively modulated by the signals modulating the I number of carriers to be inserted; and   the multiplexing means comprise an optical combiner having 2N number of inlets connected to respective outlets of the 2N number of wavelength converters.